Field of the Invention and Related Art Statement
The present invention concerns a spiral wound type membrane module used in a membrane separation device, such as a reverse osmosis membrane separation device, ultrafiltration device or microfiltration device and, more specifically, it relates to a spiral wound type membrane module in which flow channels between membranes are not clogged with suspended solids contained in raw water and the flow of raw water in the channels is disturbed to improve the permeation flow rate of permeate.
As a membrane module used for the membrane separation device such as a reverse osmosis membrane separation device, there has been known a spiral wound type membrane module in which a separation membrane is wound around the outer circumference of a water collection pipe. In such a spiral wound type membrane module, a spacer is put between membranes to form flow channel through which raw water passes and a net-like spacer has usually been employed as such a spacer.
In addition, a so-called corrugating type spacer has also been considered.
In a spiral wound type membrane module using such a net-like spacer, there is a problem that when raw water containing suspended solids is supplied, the net-like spacer suffers from clogging due to the suspended solids. Also in a spacer having V-shaped protrusions arranged in row, suspended solids are also caught at the ends of the protrusions thereby clogging the raw water flow channel.
In view of the above, it has been required to supply water to the membrane module after previously removing suspended solids from water, which required a complicated pre-treatment in the case of using the net-like spacer.
Such clogging in the raw water flow channel less occurs in the membrane module using a corrugated spacer, but linear flow channels are passed through from the inlet to the exit for the raw water in the module, in which less disturbance is given to the flow of raw water flowing between the membranes. Accordingly, the water flow in the channel tends to be a laminar flow to cause concentration polarization along with the membrane surface thereby tending to reduce the amount of permeate.
Accordingly, in the spiral wound type membrane module using the corrugated spacer, a desired amount of permeate can not be obtained unless raw water is supplied at a higher flow velocity than in the module in which net-like spacer is present, thereby bringing about a problem in view of the power cost.